Machine tools have been developed that are programmable to carry out a number of sequential operations on a workpiece, for instance, drilling a number of holes at various locations about the workpiece. A machine tool can be programmed to drill the holes at desired depths and at the proper locations in the workpiece. The machine tools are also capable of performing a sequence of different machining operations on the workpiece, such as drilling, milling, boring, etc. Such machines typically include a magazine for holding and storing the various tools utilized by the machine tool, i.e., drill bits, milling cutters, boring bars, etc. The machine tool is programmed so its spindle automatically locates a desired tool in the magazine, and then engages the tool without the need for or the assistance of a machine operator. After performing a desired operation with the selected tool, the tool is returned to the tool magazine by the spindle and automatically disengaged from the spindle, again without the assistance of or need for a machine operator.
Machine tools also have been developed that consist of multiple work stations for performing the same or different machine operations at a number of locations about the machine tool. Typically each work station includes at least one powered spindle capable of movement in virtually any direction relative to the workpiece. The workpiece can be moved from station to station as different machining operations are performed on the workpiece. To hold the workpiece stationary, the workpiece commonly is mounted on a fixture or jig having a base and clamps that secure the workpiece to the base.
Although significant advances have been made in developing machine tools capable of performing numerous sequential machine operations utilizing different tools that are automatically selected and retrieved from a tool magazine and then later returned to a tool magazine, the development of fixtures or jigs for holding and clamping a workpiece has not kept pace with advances in the machine tools. For instance, not infrequently, the clamps used to hold the workpiece during machining by a machine tool must be positioned in the direct path of a cutting tool. Each time the cutting tool approaches the clamp, the spindle holding the tool must either be retracted or stopped until the machine operator can relocate the clamp. This is not only time-consuming, but requires that the machine operator be present to perform the clamp changing operations. If the clamp is not repositioned to avoid the path of the cutting tool, severe damage can be caused not only to the cutting tool and the clamp, but also to the workpiece. Moreover, if the clamp is not relocated properly, the workpiece may shift during subsequent machine operations. Also, if the clamp is not relocated in the same location for each workpiece, then dimensional variations or errors in the workpieces may occur.
Clamping systems for machine tools have been developed wherein several individual electrically or hydraulically operated clamps are mounted on a base or jig along with a control switch or valve for actuating the clamps. One drawback of such clamping systems is that they require electrical or hydraulic supply sources that are located externally of the machine tool. The electrical and hydraulic connections to the clamping system prevent or at least hinder the jig or fixture assembly from being shuttled among different machine tools or among the various work stations of the same machine tool. The electrical and hydraulic connections also may hinder or prevent the jig or fixture from being rotated completely around or from otherwise being freely moved about during the machining process.